Unloading system for compressors



June 10, 1969 G. D. FRASER 3,443,916

UNLOADING SYSTEM FOR GOMPRESSORS Filed June 16, 1967 f CONTROL I MEANS 2s COMPRESSOR SEPARATOR INVENTOR GROVE/Q 0. FHA .SEl'? AGENT United States Patent 3,448,916 UNLOADING SYSTEM FOR COMPRESSORS Grover D. Fraser, Painted Post, N.Y., assignor to Ingersoll-Rand Company, New York, N.Y., a corporation of New Jersey Filed June 16, 1967, Ser. No. 646,607 Int. Cl. F04b 49/02 U.S. Cl. 230-24 7 Claims ABSTRACT OF THE DISCLOSURE An unloading system for an oilflooded, rotary, gas compressor having means for throttling the intake to effect desired unloading, which bleeds 01f discharge pressure, and maintains circulation of sealing and cooling oil.

This invention relates to compressor unloading systems, and in particular to an unloading system for an oilflooded, rotary, gas compressor providing for throttled unloading bleeding 01f of discharge pressure, and maintenance of oil circulation for sealing and cooling of the compressor.

Compressor unloading systems are desirable, from the standpoint of economy, in that they reduce the power requirements for the compressor when the demand'for compressed gas is low or nil. Several prior systems are known which unload the compressor to a resonable degree, however, they are usually met with a principal defect. Prior systems, on closing the intake to unload the compressor, still have pressure on the discharge side. These systems waste power by operating against a full discharge pressure. A prior system used in the field, incorporated with an oil-flooded compressor, uses an oil pump to pump out the gas trapped in the system in the unloaded condition. However, this system requires a rather complex arrangement of pluralities of valves and pipes to open and close a number of ports to have same undertake differing modes of operation. The pump which is incorporated, principally to pump oil, then must be used to pump down the trapped gas.

It is an object of the present invention to provide an improved and simplified unloading system for an oil-flooded, rotary, gas compressor.

Another object of the present invention is to provide an unloading system having a minimum of valving and piping which yet maintains circulation of sealing and cooling oil through the gas compressor.

A feature of this invention is in the use of a pressureresponsive control means to throttle the intake for desired degrees of unloading.

Another feature of this invention incorporates the use of a three-way valve to feed the compressor outlet to a bleed line.

The above-mentioned and other objects and features of this invention will become more apparent by reference to the following description taken in conjunction with the accompanying drawing, a schematic diagram of an unloading system according to my invention.

As shown in the drawing, the rotary gas compressor 1 has an inlet throttle valve 2 disposed for the inlet of gas. A separator tank 3 receives the compressed gas from compressor outlet 4 via check valve 5 and tank inlet 6. At 7 is denoted the level of oil in the tank which is fed, by means of oil line 8, three way valve 9 through cooler to pump 11 for input to the compressor for purposes of sealing and cooling thereof. Valve 9 is shown in midway position. It is movable in a clockwise direction to couple line 18 with cooler 10, and is movable in a counterclockwise direction to couple line 8 with cooler 10. In normal compressor-loaded operation, valve 9 couples line 8 with cooler 10. During the loaded mode of operaice tion, pump 11 may not be necessary as the pressure in separator tank 3 could be suflicient to cause oil flow into line 8. Outlet line 12 provides the compressed gas for work purposes and passes through secondary separator 13 which retrieves or scavenges any components of oil from the compressed gas product. Line 14 is interconnected with line 15, via three-way valve 16, to vent the scavenger out of inlet valve 2, when the system is in the loaded mode of operation. Valve 16 is shown in midway position. It is movable in a clockwise direction to couple lines 15 and 14, and movable in a counterclockwise direction to couple lines 19 and 15. In normal compressor-loaded operation, valve 16 couples lines 15 and 14. Line 17 contains the check valve 5 and interconnects the compressor outlet 4 with the tank inlet 6. Further, line 17 is joined to oil line 18 for the passage of oil therethrough, during the unloaded mode of operation, as will be explained subsequently. Line 19 is a bleed line for the compressor during unloaded operation and, as will be explained, is interconnected with line 15, via three-way valve 16, to vent the compressor output. A further oil separator 20 may be coupled in the bleed line to retrieve oil from the compressed gas bled therethrough.

A pressure-responsive control means 21 is coupled to the separtor tank 3 and inlet valve 2, via lines 22 and 23 and is further coupled to three-way valves 16 and 9. Pressure-responsive control means which can satisfy the necessary function of actuating valves 16 and 9 are both readily available, commercially, and are familiar to those skilled in the compressor control art. During loaded operation gas is taken through the inlet valve 2 into the compressor 1. Compressed gas is discharged through line 17 and check valve 5 into the separator tank 3. The oil pump 11, which is located between the cooler 10 and the oil inlet of the compressor, or the pressure differential between separator tank 3 and oil line 8, pumps oil through valve 9 and injects it into the compressor 1. The scavenger line 14 is connected to line 15, via valve 16, and vents to atmosphere out inlet valve 2. During unloaded operation the inlet valve 2 is closed off by means 21. Means 21 convey a biasing pressure, via line 23, to move a throttle valve member 24 in valve 2 against valve seat 25. Means 21 also actuate valve 16 to connect lines 15 and 19 and close line 14. The compressor discharge will thus be connected through line 19 to line 15 and vented to atmosphere. At the same time, means 21 actuates valve 9 to close line 8 and connects line 18 with the cooler 10. The pump 11 still continues to operate, and since the oil cooler 11 and line 18 are filled with oil, pump 11 draws oil which is in the cooler and line 18 therethrough and back into the compressor 1. Therefore, when the compressor 1 is operating in an unloaded condition, the discharge side of the compressor is at atmosphere and the intake side of the compressor is at a vacuum. All that is passing through the compressor is oil and a small amount of air which eliminates most of the work which must be done by the compressor.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention as set forth in the objects thereof and in the accompanying claims.

I claim:

1. A gas compressor system, comprising: a lubricantflooded gas compressor; said gas compressor having gas inlet and gas discharge means; first means coupled to said gas inlet means for throttling of same; second means coupled to said gas discharge means for removing gas trapped in said compressor upon full throttling thereof; said gas compressor further having inlet means for the input of lubricant thereto; a source of lubricant; and third means coupling said lubricant inlet means with said source; wherein said second means comprises first piping means communicating said discharge means with the atmosphere; and further including second piping means communicating said first piping means with said third means; said first and second piping means having valving means, operatively associated therewith, movable between first and second positions, for closing 011 said first piping means from the atmosphere and from said third means, in a first valving position, and for disposing said first piping means in fluid-flow communication with the atmosphere and with said third means, in a second valving position.

2. A gas compressor system, according to claim 1, wherein: said valving means comprise three-way valves, and said first means include means for controlling said valves to uncouple said third means from said lubricant source, and for communicating said third means with said second piping means.

3. A gas compressor system, according to claim 1, wherein: said third means include means for directly coupling said lubricant inlet means with said gas discharge means.

4. A gas compressor system, according to claim 1, further comprising: a fluid pump; and wherein said valving means include means for coupling said fluid pump with said gas discharge means.

5. A gas compressor system, according to claim 1, further comprising: a gas reservoir; means communicating said reservoir with said gas discharge means; wherein said gas reservoir has outlet means, and means disposed in said outlet means for scavenging lubricant thereat; and said first piping means is cooperative with said valving means to vent said scavenging means with the atmosphere.

6. A gas compressor system, according to claim 1,

wherein: said first means comprise a throttling valve disposed in advance of said gas inlet means, and means coupled to said throttling valve for controlling the throttling thereof.

7. A gas compressor system, according to claim 1, wherein: said second piping means comprises a bleed line through connecting said gas discharge means with the atmosphere.

References Cited WILLIAM L. FREEH, Primary Examiner.

WARREN J. KRAUSS, Assistant Examiner.

U.S. C1. X.R. 230-31 

